A Korean research team announced findings that when bacteria living in the mouth settle in the gut, they can affect neurons in the brain and potentially cause Parkinson's disease.
A research team led by Ko Ara, a professor in the Department of Life Sciences at Pohang University of Science and Technology POSTECH, said on the 19th that, together with teams led by Lee Yeon-jong, a professor at Sungkyunkwan University School of Medicine, and Kim Han-joon, a professor at Seoul National University College of Medicine, they identified the mechanism by which oral bacteria trigger Parkinson's disease through metabolites produced in the gut. The findings were published online on 5th in the international journal "Nature Communications."
Parkinson's disease is a degenerative brain disorder in which dopamine neurons, responsible for involuntary muscle movement, decrease, causing tremors in the hands and feet and a heavy gait. It is also a common disease affecting 1% to 2% of the global population aged 65 and older. It has been known that the bacteria in the guts of patients with Parkinson's disease differ from those of healthy people, but the details had not been clarified.
The team first analyzed the gut microbiota of patients with Parkinson's disease and confirmed an abnormally high level of Streptococcus mutans, one of the oral bacteria that cause cavities. The enzymatic metabolites called "urocanate reductase" and "imidazole propionate," produced by this bacterium, were also detected in large amounts in the blood of patients with Parkinson's disease.
Next, when they colonized the guts of laboratory animal models with Streptococcus mutans or injected engineered Escherichia coli expressing urocanate reductase, the concentration of imidazole propionate increased markedly in the animals' blood and brain tissue. This shows that imidazole propionate produced in the gut can travel through the bloodstream to the brain and accumulate there.
In this process, key symptoms of Parkinson's disease also appeared. Destruction of dopamine neurons, neuroinflammation, and impaired motor function were observed. Aggregation of "alpha-synuclein," a representative pathological protein of Parkinson's disease, was also promoted, accelerating disease progression. This shows that metabolites produced by specific gut microbes can act as risk factors.
The researchers also confirmed that this pathological process depends on the activation of mTORC1, an intracellular signaling protein, and that administering an mTORC1 inhibitor suppresses these phenomena.
Professor Ko Ara said, "We have identified a new Parkinson's disease onset pathway that links the oral cavity, gut, and brain," noting, "This study is also significant in that it shows the potential for developing new therapeutics targeting the gut microbiota."
References
Nature Communications (2025), DOI: https://doi.org/10.1038/s41467-025-63473-4